assessing a non-acute total coliform rule violation at ... · release of free ammonia biological...

Assessing a Non-Acute Total Coliform Rule Violation at

Portland Water Bureau: What Happened, What Worked,

What Didn't, & Why? Part 2 of 2

PNWS AWWA Annual Conference

April 30th, 2015

Bellevue, WA

Presented by: Melinda Friedman, P.E.

Amie Hanson, P.E. Confluence Engineering Group, LLC

Presentation Overview

Coliform Occurrence Pathways

Conditions that May Have Contributed to TCR Event

Water Quality

O&M

Effectiveness of Mitigation Strategies

Recommendations

2

Independent Desk-Top

Review of Available

Information

Coliform Occurrence Pathways

Source water/treatment breakthrough

Direct contamination of the distribution system

Regrowth in biofilms/sediments

Sample tap contamination/sample collection issues

3

Coliform Occurrence Pathways - Findings Source water/treatment breakthrough

No turbidity event

No issues with CTs

Localized

Direct contamination of the distribution system

No pressure events

No main breaks/repairs

No fires

No construction

CC inspections up to date

Regrowth in biofilms/sediments

Warm water (≥ 15oC)

Very low chlorine

Nitrification event

Lots of unlined cast iron pipe

Sample tap contamination/sample collection issues

Positives at many different types of sample taps

Different sample collectors

Confirmed sampling protocols

4

What Water Quality Conditions May Have Contributed to the Biofilm/Regrowth TCR Event?

5

Assessment of Water Quality & System Conditions

Key water quality issues that can contribute to

regrowth/biofilms:

Chlorine residual maintenance

DS temperature

Nitrification

Residual loss

pH

ORP

Nutrients

Ammonia

AOC

Iron/Mn etc.

6

Total Chlorine - Findings

7

Total Chlorine levels were significantly lower in TC + samples

8

Temperature- Findings

Average monthly temperatures highest in Bertha and Stephenson,

but not higher in 2013 compared to previous years

Temperatures ≥ 15C July/Aug/Sept/Oct

9

Overview of Nitrification Process

Chloramine demand/decay

Release of free ammonia

Biological oxidation to nitrite and

nitrate

Overall reaction for complete nitrification (Grady et al. 1999)

NH4+ + 1.856 O2 + 1.979 HCO3

-

0.0205 C5H7O2N + 0.979 NO3- + 1.041 H2O + 1.876 H2CO3

Disinfectant residual loss

Decreased dissolved oxygen

Decreased alkalinity

Decreased pH

Lowers ORP

which impacts

stability of cast

iron scales!!!

Effect of Oxidation-Reduction Potential (ORP) Plunge

11

During Nitrification

PWB Typical

12

What Operations & Maintenance Activities May Have Contributed to a Biofilm/Regrowth TCR Event?

13

O&M Activities - Flushing

Spot flushing

May have stirred up and released biofilm containing coliform

bacteria to bulk water

No valve isolation

Water flows to open hydrant from multiple directions

Can’t control velocities in adjacent mains with different diameters

If poor water quality had come from Marquam Tank, may have

pulled further into distribution system

Lack of Aggressive UDF Program in Problem Areas

Allowed for accumulation of biofilm and sediments

Increases chloramine demand

14

Comparison of bacterial abundance in an unchlorinated distribution system in the Netherlands – 4-Inch PVC pipe

15 Source: Liu et al., 2014

O&M Activities - Findings

Does not appear that the TCR event was caused by direct contamination due to main repair/installation, pressure event, cross-connection, etc.

However, O&M practices may have contributed to water quality conditions that support regrowth, biofilm sloughing, etc.

16

Effectiveness of Mitigation Strategies

17

Mitigation Strategies Used

Tank O&M strategies

Increased disinfection - boosting

Spot flushing

Proactive and reactive

UDF

18

Tank Strategies

Deep cycling - Marquam Hill 2 rebounded rapidly

Chlorine increased

Nitrate, nitrite, HPC decreased

However, appears to have caused negative water quality impact

downstream…

Appropriate to take Marquam 1 and Bertha off line

Reduced overall water age in the area

Prevented additional lower quality water from reaching area

19

System-Wide Chloramine Boosting

Residual boosted from 1.8 to 3.0 mg/L at Lusted Hill on 10/2/13

Increases measured at Burlingame, Arnold, and Vermont pressure zones within a week

Did not reach goal of 1 mg/L at Bertha WQSS 182 for two months

Consistently detectable residuals appeared within 3 weeks - 1

month

Difficult to overcome water age and existing chlorine demand

Can’t necessarily rely on system-wide boosting to be timely, effective site-specific strategy given current water age and pipe conditions

20

Spot Flushing

21

22

23

WQ and O&M Recommendations

24

Chloramine Residual Boosting

Imperative to maintain adequate residuals

Immediate:

Conduct seasonal boosting at Headworks during early summer

and continue through nitrification season

Longer Term:

Consider boosting at applicable tanks

Faster response in problem areas

Fewer DBPs

25

Unidirectional Flushing

Important as a proactive and reactive tool

Program needs (and has since gained) ownership and management

Continue with development, implementation, evaluation, and refinement of program

PWB and SPU have submitted a proposal to WRF to study flushing as a corrective action under the RTCR

Prioritize problem areas of distribution system

26

TCR Response, Management, and Communications

PWB staff indicated good and positive communications during the event

Teamwork

Timely decision making

No road blocks

Develop and add a TCR Decision Tree to current TCR Plan

Suspected source water/treatment breakthrough

Suspected regrowth

Suspected contamination

Suspected sample tap/contamination issue

27

Conclusions

PWB data availability key to understanding trends

TC+ violation appears to have been cause by a regrowth event

Conditions in 2013 not unique to PWB and probably similar in

portions of wholesaler systems with similar conditions!

No indications of distribution system contamination

Nitrification may have contributed to water quality conditions that

favor regrowth

Spot flushing was not an effective response strategy given water

quality conditions

UDF and boosting were more effective

Proactive measures proven to be more effective than reactive

measures

28

Questions?

Presented By:

Melinda Friedman, P.E.

Confluence Engineering Group, LLC

melinda@confluence-engineering.com

206.527.6832

www.confluence-engineering.com

Coliform Occurrence Pathways

Source water/treatment breakthrough

Direct contamination of the distribution system

Regrowth in biofilms/sediments

Sample tap contamination/sample collection issues

30

Source Water/Treatment Breakthrough

Coliform presence could occur if:

Contamination of sources

Treatment upset allowing microbial contamination to reach the DS

Unusual turbidity event

Would expect coliform presence to be more widespread throughout the system

Positive samples were extremely localized

No indications of CT violations or issues

No unusual weather or turbidity issues

31

Seems Unlikely…

Direct contamination of the distribution system - Findings

Pressure maintenance and associated facilities

Pressure loss: No alarms or complaints before event

Valves: Inspections - none identified in wrong position

Main breaks/repairs

None occurred in area leading up to event

Cross-connections

Always possible…

Inspections - none identified

Storage facilities

Inspections discovered one missing screen on Bertha overflow

Construction

None occurred in area leading up to event

E. coli not present in any samples

32

Seems Unlikely…

Regrowth in Biofilm/Sediments Microorganisms already present in the distribution

system experience a “growth spurt” because water

quality conditions are optimal

Optimal water quality conditions for regrowth:

Warmer temperatures (>15 degrees C)

Low to no disinfectant residual in DS

Increased nutrients

Unlined cast iron piping present in affected area

UCI served 25 of 27positive sample sites (92.6%)

40 of 42 positive samples (95.3%)

No systematic UDF or routine pipe cleaning program in

the west side of system

33

Seems Likely…

Sample Tap Contamination/Sample Collection Issues - Findings

Sample Tap Contamination

Initial repeat samples at WQSS 200 - negative

Many positives appear in localized area, not only at WQSS 200

It is difficult to ensure integrity of repeat sampling sites

Sample Collection

Multiple personnel collected samples

PWB confirmed sampling practices

34

Seems Unlikely…